The Physics
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Angular Speed of the Earth

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Serway, Raymond A., Beichner, Robert J., Jewett, John W. Physics for Scientists and Engineers with Modern Physics: Fifth Edition. Orlando, FL: Saunders College Publishing, 2000: 317 Q10. "Find the angular speed of the Earth's rotation on its axis
2π radians/86,400 seconds"
7.27 × 10−5 rad/s
World Book Encyclopedia Vol 6. Illinois: World Book Inc.: 1984: 12. "It takes 23 hours 56 minutes 4.09 seconds for the Earth to spin around once 2π radians/86164.09 seconds" 7.2921159 × 10−5 rad/s
Cohen, Homer. Radian per second. "We might say that the Earth rotates at 7.272 × 10−5 rad/s, and this tells us its angular speed" 7.272 × 10−5 rad/s
World Book Encyclopedia Vol 5. Illinois: Field Enterprises Educational Corporation:1961: 13. "17.5 miles a minute at the equator is the speed of the earth. 0.0044 rad/min" 7.367 × 10−5 rad/s
Bulletin B: Earth orientation parameters. International Earth Rotation Service. [see table below] 7.292115090 × 10−5 rad/s
Date    (0h UTC) DR          OmegaR
2002 MJD s (microrad/s)
APR 5 52369 .00083 72.921 15076
APR 10 52374 .00079 15080
APR 15 52379 .00067 15090
APR 20 52384 .00059 15097
APR 25 52389 .00066 15091
APR 30 52394 .00067 15090
MAY 5 52399 .00067 15090

The planet Earth has three motions. It rotates about its axis, giving us day and night. The earth also revolves around the sun, this revolution gives us two basic weather patterns (cold and hot). The earth also moves through the Milky Way along with the rest of the Solar System.

It takes the Earth approximately 23 hours, 56 minutes and 4.09 seconds to make one complete revolution (360 degrees). This length of time is known as a sidereal day. The Earth rotates at a moderate angular velocity of 7.2921159 × 10−5 radians/second. Venus has the slowest angular velocity (2.99 × 10−7rad/sec) and Jupiter has the fastest (1.76 × 10−4rad/sec).

The graph below shows that relationship between the days and the length of day. Starting with January 5th up until June 5th it shows the length of the days and how the days have been getting shorter.

Click for a larger image or to view the raw data file.
Source: IERS Bulletin B 167 (3 January 2002)

As a result of variation in gravitational forces due to the moon, the sun and other planets in the solar system, displacements of matter in different in different parts of the planets and other excitation mechanisms, the rotational speed of the Earth about its axis varies in time. Recently, days have been getting shorter by hundredths of a second, which implies that the angular velocity of the Earth has been increasing. The factors causing this increasing in the Earth's rotational velocity have not been determined.

Jason C. M. Atkins -- 2002

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Data and Story Project
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